Ion Plasma Mode Research Articles

Electrostatic wave modulation in collisional pair-ion plasmas

The effects of ion-neutral collision on the electrostatic wave packets in the absence of the magnetic field in a pair-ion plasma have been investigated. Considering a two-fluid plasma model with the help of the standard perturbation technique, two distinct electrostatic modes have been observed, namely, a low-frequency ion acoustic mode and a high-frequency ion plasma mode. The dynamics of the modulated wave is governed by a damped nonlinear Schrödinger equation. Damping of the soliton occurs due to the ion-neutral collision. The analytical and numerical investigation reveals that the ion acoustic mode is both stable and unstable, which propagates in the form of dark solitons and bright solitons, respectively, whereas the ion plasma mode is unstable, propagating in the form of a bright soliton. Results are discussed in the context of the fullerene pair-ion plasma experiments.

Phase-mixing of ion plasma modes in pair-ion plasmas

Nonlinear interaction between two electrostatic normal modes of a warm pair-ion plasma, viz., ion plasma mode (Langmuir mode) and ion acoustic mode has been analyzed by employing a perturbation technique. It is shown that a gradual loss of phase coherence in the excited Langmuir wave dynamics (phase-mixing) occurs in such a plasma, leading to wave-breaking at arbitrarily low wave amplitudes. Nonlinear results provide an approximate expression for the phase-mixing time which is found to increase with the increase of the ratio of acoustic frequency to Langmuir frequency. The results of our investigation are expected to be relevant to the laboratory produced paired fullerene-ion plasmas.

Non-stationary Coulomb crystals in linear Paul traps

Ion Coulomb crystals form when trapped ions are cooled below a certain criticaltemperature. In radiofrequency (RF) traps, such crystals are usually stationary(i.e. non-rotating) with shapes similar to those of cold, homogeneously chargedliquids when the number of ions is sufficient for three-dimensional structures toappear. ‘Dynamically stable’ structures can, however, also be created either bydirectly applying a torque to an initially stationary crystal or by choosing trapparameters just within the stability region where stationary crystals will melt dueto parametric resonances between the RF trap field and ion plasma modes.

Interaction of crossed laser beams with plasmas

The parametric interaction of two crossed collimated laser beams with ion plasma modes has been studied. The underlying process is a density grating that is created by the two laser beams. The Bragg diffraction that is produced enhances forward stimulated Brillouin scattering (SBS) which results in a time dependent energy exchange between the two beams. A diversity of other SBS processes which depend on the symmetry of driving laser beams are also discussed.

Stimulated Brillouin scattering and ponderomotive self-focusing from a single laser hot spot

The parametric interaction of a focused Gaussian laser beam with ion plasma modes has been studied by using two dimensional nonparaxial spectral code [Phys. Fluids B 5, 3748 (1993)]. It is shown that the reflectivity of stimulated Brillouin scattering (SBS) from the single laser hot spot is dominated by backscattering. The reflectivity scales with the stationary gain coefficient and very closely follows predictions of a simple three wave coupling model. This is in spite of essentially nonlinear SBS behavior, which develops in the inhomogeneous density channels formed by the ponderomotive force of the beam, where it competes with the self-focusing instability (SFI). For the relatively short focal lengths (f/number<10) the SFI is diffraction limited and evolves until hot spot is focused to a size of few laser wavelengths. The SFI is responsible for the broad and anisotropic angular distribution of the transmitted light.

Two-dimensional studies of stimulated Brillouin scattering, filamentation, and self-focusing instabilities of laser light in plasmas

The parametric interaction of an intense laser beam with ion plasma modes in a two-dimensional Cartesian geometry has been studied for the first time by avoiding the paraxial optics approximation. This model allows investigation of the competition between forward, sideward, and backward stimulated Brillouin scattering (SBS) along with filamentation and self-focusing instabilities. It is shown that the SBS saturation level, the angular distribution of transmitted and scattered light, and their temporal dependence are governed mainly by two control parameters: the backward SBS gain coefficient G, and the ratio αsf of the incident beam power to its critical value for the onset of self-focusing. In the case of large values of G≳15, backward SBS dominates and prevents both self-focusing and forward SBS. For smaller values of G, the interaction exhibits a complex oscillatory behavior, which corresponds to the competition between backward and forward SBS for αsf≲1, and involves also self-focusing for higher beam intensities.

Spectrum of low frequency modes in strongly coupled plasmas

A generalized hydrodynamic model is applied to study the low frequency dielectric function in degenerate strongly coupled plasmas. The dispersion and damping of ion acoustic and ion plasma modes are presented in an explicit form. New features of the collective mode structure are established and discussed.

Electronic screening in one-component plasmas: Collective-mode structure.

The Golden-Kalman velocity-average approximation scheme for one-component plasmas is generalized to account for electronic screening effects. New formulas are established for the dispersion and damping of the ion-sound and ion-plasma modes at arbitrary coupling.

Modulational stability of the ion plasma mode

The cubic Schrödinger equation satisfied by the slowly varying amplitude of the longitudinal wave in an electron-ion plasma is deduced using the method of Kakutani and Sugimoto. The analysis of the Schrödinger equation shows that the ion acoustic wave is modulationally stable and that the ion plasma oscillations are modulationally stable or unstable according to whether the wavenumber is below or above a critical value which is controlled entirely by the wave dispersion.

Decay Instability of the Ion Acoustic Wave

The parametric excitation of the longitudinal, plasma mode and the transverse, electromagnetic mode in a warm, uniform plasma is investigated for the case in which the pump wave is another electromagnetic mode. The three interacting waves are assumed to propagate in the same direction. The longitudinal mode has two branches, namely, the electron plasma mode and the ion plasma mode. The parametric coupling of the longitudinal and the transverse waves in the presence of the pump wave leads to instabilities of the interacting waves. Illustrative numerical results are presented for the parametric instabilities of the electron plasma oscillation which is a part of the electron plasma mode and those of the ion acoustic waves and the ion plasma oscillations which are parts of the ion plasma mode. The ion acoustic wave is efficiently excited when the pump and the idler wave frequencies are approximately equal to one and a half times the electron plasma frequency.

Electromagnetic and Electroacoustic Mode Radiation Resistance of Linear Antennas in Compressible Electron-Ion Plasma

Expressions for the field intensity in the two-component (electron-ion) plasma for both types of modes, electromagnetic and electroacoustic pertaining to a dipole source with sinusoidal current distribution having a general propagation constant, have been given in the present paper and from these field expressions, the radiation resistance of the finite sized dipole for the respective modes is evaluated. Comparing the fields with the corresponding ones in single component (electron) plasma, it is observed that the electromagnetic field is identical in form and differ slightly in magnitude on account of inclusion of an additional term for ions. But the electroacoustic field consists of two parts corresponding to the two pressure modes, namely the modified electron plasma mode and the modified ion plasma mode. The electromagnetic and electroacoustic fields and radiation resistances of a dipole in one-component (electron) plasma can be derived as a particular case from the general results of this paper by neglecting the ion motion.

Wave Propagation in Compressible Electron-ion Magnetoplasma†

ABSTRACT Coupled wave equations have been developed for the propagation of electromagnetic, electron acoustic and ion acoustic waves in a homogeneous, warm magnetoplasma employing the linearized two-fluid continuum theory of partially ionized plasma dynamics. For the purpose of this study propagation is considered in a plane transverse to the static magnetic field. Coefficients occurring in the dispersion relation have been calculated for two-component electron-ion hydrogen magnetoplasma over a wide frequency spectrum and these are used to study the dispersion relation in various frequency ranges. It is observed that the modified ion plasma mode propagates in the entire range of the frequency spectrum but the electromagnetic mode, ordinary as well as extraordinary, and the electron-plasma mode propagate only in the range higher than the electron plasma frequency.

Radiation propagating transverse to the external magnetic field from an electromagnetic source in an unbounded plasma

The radiation characteristics of a line source of magnetic current embedded in an unbounded plasma are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The plasma is assumed to be a homogeneous and macroscopically neutral mixture of compressible gas of electrons and ions. A two-fluid continuum theory of plasma dynamics is employed. It is shown that it is possible to define three suitable wave functions which satisfy separately simple wave equations whose solutions are written down by inspection. These wave functions specify the three possible modes which are identified, respectively, to be the modified forms of the electromagnetic, the electron plasma and the ion plasma modes. The limiting behavior of these modes are discussed for the following two cases: 1) infinite source frequency and 2) vanishing external magnetic field. The dispersion relations for the three modes are examined in detail for the general case using a perturbation procedure. It is shown that the modified ion plasma (MIP) mode propagates for all frequencies whereas both the modified electron plasma (MEP) mode and the modified electromagnetic (MEM) mode have a low-frequency cutoff. Explicit expressions for the cutoff frequencies are obtained. The power radiated in each of the three modes is also evaluated. It is found that the power radiated in the MEM mode is always lower than that due to the line source in free space, whereas the power radiated in the two plasma modes is higher than that value for certain ranges of frequency.

Radiation from electromagnetic sources in a plasma

The radiation from electromagnetic sources in an unbounded, isotropic plasma is treated. Using a two-fluid magnetohydrodynamic approach, the problem is formulated in terms of three orthogonal modes, namely, i) the electromagnetic mode, ii) the electron plasma mode and iii) the ion plasma mode. When formulated in this manner, the radiation from simple electromagnetic sources are obtained easily. Three specific sources are treated, namely, i) a point source of electric current, ii) a uniformly moving charge and iii) a short filament with prescribed current distribution. For the case of the electric dipole and the current filament, the total power radiated in each of the three modes are obtained. A point charge moving uniformly with the velocity of sound, for example, is found to excite only the ion plasma mode. The frequency and the angular spectrum of the emitted radiation are obtained. It is found that at frequencies less than a critical frequency which is approximately equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sqrt{2}</tex> times the ion plasma frequency, the radiation has the character of a simple sound wave.